Conventional skidders or skidder machines are large articulated heavy duty tractor vehicles for pulling, lugging, dragging, lifting or otherwise removing down timber from the woods. Such skidders are characterized by their large size, heavy weight, large tractor tires, and maneuverability and are of two basic types.
The cable skidder is a large tractor vehicle which incorporates a winch and a timber skidding cable that rides over fairlead rollers mounted on an arch for cable skidding, dragging, pulling, or hauling down timber by cable winching. Multiple chokers are mounted on the end of the skidder cable, generally one for each tree or trunk to be hauled at once. The chokers are relatively shorter lengths of cable chokers or chain chokers for cinching around the end of a tree or trunk and are coupled to sliders or slider collars that slide on the main skidder cable. For example up to 10 chokers may be mounted on the end of the skidder cable for dragging and hauling multiple trees or trunks. After cable winching and dragging timbers to the skidder, the butt ends of the timbers are lifted on the cable for hauling by the skidder.
A grapple skidder is a large tractor vehicle on which a boom is mounted at one end on a pivotal mounting for pivotal motion of the boom upward and downward. A grapple or large jaw is mounted at the free end of the boom for lifting the end of a tree or trunk for towing, skidding, and hauling the down timber from the woods. The grapple jaw may be large enough when open, for example, 4 feet (1.2 m) in width at the mouth to accommodate multiple trees or trunks for grapple skidding.
A disadvantage of the conventional skidder tractors whether cable skidders or grapple skidders is the large size and heavy weight, for example typically 10 tons for even the lighter weight skidders. The heavy weight, large size, and large tractor tires result in substantial disruption of and damage to the forest floor, soil and undergrowth. The traditional skidders are notorious for the soil erosion problems and disruption resulting from skidder operations.
Another disadvantage of even the smallest available skidder machines is the substantial cost in the order of at least $75,000 to $80,000 in the lower price range. This places a heavy financial burden on the small woods operators and independent contractors. A major portion of the woods harvesting and skidding is contracted out by the paper companies and timber companies to the small woods operators and independent contractors. The heavy financial burdens result in equally heavy operation of the skidder machines in order to meet financing payment obligations. The conventional skidder machines are furthermore out of reach of the small wood lot owners who either cannot justify the cost or refuse to permit the disruption and damage associated with conventional skidder machine operation.
A variety of power wagons or power trailer wagons are described in prior art patents. For example the Dion U.S. Pat. No. 3,473,619 describes a drive unit such as a track vehicle and a power driven wagon for transporting logs with a drive coupling between the track vehicle and power driven wagon. The internal combustion engine 14 is located in the drive vehicle or track vehicle and the drive train power coupling includes separate differential units 38 and 40 in the drive vehicle and driven vehicle with three 5 universal joints 41, 42 and 43 located in between to permit universal motion of the driven wagon relative to the driving track vehicle.
Another positively driven trailer wagon is illustrated in the Berger U.S. Pat. No. 3,442,345. As in the Dion patent, differentials 20 and 22 are included in both the forward cab of the drive vehicle and the following trailer portion. The drive shaft connects the forward and rear differentials with universal joints at each end.
The Boggess U.S. Pat. No. 2,959,236 provides a more detailed description of a universal trailer drive train including a universal swivel gear unit, universal joints, and telescoping drive shafts. The Ritter U.S. Pat. No. 2,903,080 describes a power driven or positively driven trailer wagon with detailed description of a complex differential drive means.
A number of other arrangements are described for power take-off positive drive for trailing wagons and vehicles including the more recent Gego et al. U.S. Pat. No. 4,069,885 and the early Hunt U.S. Pat. No. 721,705.
While the concept of a positively driven power trailer wagon for a variety of applications is old, no one has used the tractor power take-off for a trailed skidder vehicle providing a light weight equivalent of a skidder or skidding machine for cable winching, grappling, skidding and hauling tree length timbers. The novel structural features required for timber hauling skidder functions and applications on a trail vehicle are not disclosed in the references. Nor is it apparent how a trailed or trailing vehicle may be particularly adapted for such timber skidding and hauling functions and applications.